Dillon refuses to officially support this caliber. Third-party conversion kits sometimes available for 550 only on Five Seven Forum
Request a new caliber
Note: Please do not submit requests for 650 or 1050 versions of 550 conversions. Contact Dillon directly!
Dillon makes many 550 conversions that they do not make for their other presses.
They're more likely to produce the conversion you want if a lot of people write them asking for it.
They're very unlikely to do anything if I just write them saying some guy from the internet wants it!